Polymer powder and object made from the same

ABSTRACT

A powder composition suitable for use in selective laser sintering for printing an object. The powder composition includes a first fraction including a plurality of polyaryletherketone (PAEK) particles having a mean diameter less than 30 microns, a second fraction having a plurality of polyaryletherketone (PAEK) particles having a mean diameter greater than 30 microns, and a third fraction having a plurality of carbon fibers. The first fraction and the second fraction are formed by an air classification separation performed on a pulverized powder. After the separation, the first fraction, the second fraction, and the third fraction are blended in a high intensity mixer. The powder composition when used in selective laser sinter results in parts with increased tensile strength and reduced surface roughness, among other improvements, as compared to similar powders omitting the first fraction. The PAEK may include polyetherketoneketone (PEKK).

TECHNICAL FIELD

The present disclosure generally relates to additive manufacturingtechnology and techniques, and more specifically relates to a polyetherether ketone (“PEKK”) powder composition for use in selective lasersintering (“SLS” or “LS”), a method for preparing the powdercomposition, and a method for additively manufacturing an object usingthe PEKK powder composition such that the useful yield of the powdercomposition is increased.

BACKGROUND

It is known to use additive manufacturing technology and techniques,together with polymer powders, to manufacture high-performance productshaving applications in various industries (e.g., aerospace, industrial,medical, etc.).

SLS is an additive manufacturing technique that uses a laser to fusesmall particles of plastic, metal (direct metal laser sintering),ceramic, or glass powders into a mass having a desired three-dimensional(3-D) shape. The laser selectively fuses the powder material by scanningcross-sectional layers generated from a 3-D digital description of thedesired object onto the top layer of a bed of the powder material. Aftera cross-sectional layer is scanned, the powder bed is lowered byone-layer thickness in a z-axis direction, a new top layer of powdermaterial is applied to the powder bed, and the powder bed is rescanned.This process is repeated until the object is completed. When completed,the object is formed in a “cake” of unfused powder material. The formedobject is extracted from the cake. The powder material from the cake canbe recovered, sieved, and used in a subsequent SLS process.

Polyaryletherketones (“PAEK”) are of interest in the SLS process becauseparts that have been manufactured from PAEK powder or PAEK granulatesare characterized by a low flammability, a good biocompatibility, and ahigh resistance against hydrolysis and radiation. The thermal resistanceat elevated temperatures as well as the chemical resistancedistinguishes PAEK powders from ordinary plastic powders. A PAEK powdermay be a powder from the group consisting of polyetheretherketone(“PEEK”), polyetherketoneketone (“PEKK”), polyetherketone (“PEK”),polyetheretherketoneketone (“PEEKK”) or polyetherketoneetherketoneketone(“PEKEKK”).

PEKK powders are of particular interest in the SLS process becauseobjects that have been manufactured from PEKK powders via SLS havedemonstrated not only the above characterizations but also superiorstrength relative to other PAEK materials. Furthermore, PEKK powders areunique in the SLS technique because unused PEKK powder can be recycledin subsequent SLS processes and the resultant pieces exhibit increasedstrength as compared to similar parts made with virgin powder.

In order to prepare the PEKK powder, raw PEKK is milled to form a PEKKpowder. The grinding step can be performed using known grindingtechniques, for example jet milling, by companies such as Aveka, Inc. ofWoodbury, Minn., USA. Upon completion of the grinding step, the powderparticles typically range in size from 8 μm to 160 μm, as determined bypost-milling measurement.

A disadvantage of performing SLS on powder compositions with PEKK isthat it is not possible to build objects when fine particles areincluded in the feedstock. Fine particles, typically described in thiscontext, have a diameter of 30 μm or less and are sometimes referred toas fines. It is not possible to use the fines in SLS because theyinhibit the application of powder in the SLS machine. For example, thefines may cause pilling, sticking, and other forms of fouling in stepsof the SLS process in which smooth flowing powder are required.Therefore, it is understood that it is not possible to operate the SLSmachine to build parts using milled powder that includes fine particles.

It is known to overcome the aforementioned disadvantages associated withmilled SLS feedstocks by removing the fines from the feedstock prior touse in the SLS procedure. The removal of fine particles can be achievedby identifying a cut off size, for example 30 μm, and sieving particlesbelow this identified value from the milled feedstock via an airclassification or other method so as to remove the problematic particlesfrom the lot.

US Publication No. 2015/0328665 to Hexcel Inc. for a Method forPreparing Fine Powders for Use in Selective Laser Sintering Processesacknowledges that fine powders cannot be used in the SLS process andfurther discloses the methods of eliminating fines from the feedstocksprior to performing SLS.

US Publication No. 2006/0134419 to Monsheimer et al. for Use ofPolyarylene Ether Ketone Powder in a Three-Dimensional Powder-BasedMoldless Production Process, and Moldings Produced is directed to apowder containing a porous PAEK whose BET surface area is from 1 to 60m²/g in the SLS process. Monsheimer teaches that for betterprocessability in a rapid prototyping or rapid manufacturing system, thefraction of particles smaller than 30 μm should eliminated from themilled particle feedstock via sifting. U.S. Pat. No. 8,795,833 toDallner et al for Polyoxymethylene Laser Sintering Powder, Process forIts Production, and Moldings Produced from This Laser Sintering Powderteaches that particles with size smaller than 30 μm (fines) are removedfrom the ground product prior to SLS. US Publication No. 2017/0028632 toCox for Powder Bed Fusing Thermoplastic Polymers explains that finesthat are generated during the milling process cannot be used in SLS. USPublication No. 2018/0009982 to Steel for compounded copolyimide powdersfor use in SLS teaches removal of the fines fractions for improvedflowability in the SLS process.

Another disadvantage resulting from the need to remove fine particlesfrom the polymer feedstock prior to SLS is that it significantlyincreases the cost of performing SLS because there is no commercialdemand for the fine particles separated from the feedstock during thesieving process and therefore they are considered waste. The removal offine particles prior to SLS reduces the yield of materiel generatedduring the milling process, sometimes by up to 33%, and thus increasesthe cost of parts made via SLS.

SUMMARY

The needs set forth herein as well as further and other needs andadvantages are addressed by the present teachings, which illustratesolutions and advantages described below.

It is an objective of the present teachings to remedy the abovedrawbacks and issues associated with prior art selective laser sinteringmethods.

The present invention resides in one aspect in a powder compositionsuitable for use in laser sintering for printing a three-dimensionalobject. The powder composition includes a first fraction comprising apolyaryletherketone (PAEK) powder having a plurality of particles, theplurality of particles having a mean diameter less than 30 micron. Thepowder composition includes a second fraction comprising a PAEK powderhaving a plurality of particles, the plurality of particles having amean diameter greater than 30 microns. The powder composition includes athird fraction comprising a plurality of carbon fibers.

In yet a further embodiment of the present invention the first fractionand the second fraction comprise polyetherketoneketone (PEKK) particles.

In yet a further embodiment of the present invention the plurality ofparticles of the first fraction have a mean diameter between 10 μm to 20μm.

In yet a further embodiment of the present invention the third fractionis between 10% and 20% of the composition by weight.

In yet a further embodiment of the present invention the first fractionis between 10% and 20% of the composition by weight.

In yet a further embodiment the first fraction is 17% or less of thecomposition by weight. In some embodiments, the first fraction is 10% orless of the composition by weight, and in yet further embodiments thefirst fraction is 8.5% of the composition by weight.

In yet a further embodiment of the present invention, the third fractionis 15% of the composition by weight.

In yet a further embodiment of the present invention the first fractionis 15% of the composition by weight.

In yet a further embodiment of the present invention the PEKK particlesare substantially non-spherical.

In yet a further embodiment of the present invention a mean length ofthe plurality of carbon fibers is greater than a mean diameter of theplurality of particles of the powder composition.

The present invention resides in one aspect in a method of preparing apowder composition suitable for use in laser sintering for printing athree-dimensional object. The method includes the step of providing apolyaryletherketone (PAEK) powder material comprising a plurality ofparticles. The method further includes the step of separating theplurality of particles based on a particle diameter to form a firstfraction and a second fraction. The first fraction has a plurality ofparticles having a mean diameter less than 30 micron. The secondfraction has a plurality of particles having a mean diameter greaterthan 30 microns. The method next includes the step of mixing the firstfraction with the second fraction with a plurality of carbon fibers toobtain the powder composition suitable for use in selective lasersintering.

In yet a further embodiment of the present invention the step ofproviding PAEK powder comprises the step of providing a plurality ofpolyetherketoneketone (PEKK) particles.

In yet a further embodiment of the present invention the plurality ofparticles of the first fraction resulting from the step of separatinghave a mean diameter between 10 μm to 20 μm.

In yet a further embodiment of the present invention the third fractionis between 10% and 20% of the composition by weight resulting from thestep of mixing.

In yet a further embodiment of the present invention the first fractionis between 10% and 20% of the composition by weight resulting from thestep of mixing.

In yet a further embodiment of the present invention the third fractionis 15% of the composition by weight.

In yet a further embodiment of the present invention the first fractionis 15% of the composition by weight.

In yet a further embodiment of the present invention the method includesthe step of grinding a PEKK stock to form the PEKK particles, the PEKKparticles being substantially non-spherical.

In yet a further embodiment of the present invention, the step mixingcomprises mixing the first fraction, the second fraction, and the thirdfraction in a high intensity mixer.

In yet a further embodiment of the present invention the step of mixingcomprises operating the high intensity mixer at a speed of greater than500 rpm for at least one minute.

In yet a further embodiment of the present invention, the methodincludes the step of heat treating the PEKK stock before the grindingstep to evaporate impurities.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a LS machine in accordance with one embodiment of thepresent invention.

FIG. 2A is an image showing a magnified view of a plurality of PEKKparticles.

FIG. 2B is an image showing a magnified view of a plurality of PEKKparticles and a plurality of carbon fibers.

FIG. 3A is a chart showing a particle size distribution (“PSD”) byparticle count of a PEKK particle feedstock after milling and beforeseparation.

FIG. 3B is a chart showing a PSD by particle volume of a PEKK particlefeedstock after milling and before separation.

FIG. 4A is a chart showing a PSD by particle count of a plurality ofPEKK fine particles separated from the PEKK feedstock shown in FIGS. 3Aand 3B after milling.

FIG. 4B is a chart showing a PSD by particle volume of a plurality ofPEKK fine particles separated from the PEKK feedstock shown in FIGS. 3Aand 3B after milling.

FIG. 5A is a chart showing a PSD by particle count of a plurality ofPEKK particles in the PEKK feedstock shown in FIGS. 3A and 3B after thefine particles have been separated.

FIG. 5B is a chart showing a PSD by particle volume of a plurality ofPEKK particles in the PEKK feedstock shown in FIGS. 3A and 3B after thefine particles have been separated.

FIG. 6 is a table showing properties of different powder compositions.

FIG. 7A is a table showing additional information and propertiesregarding the powder compositions referenced in FIG. 6.

FIG. 7B is a table showing selective laser sinter parameters of buildjobs using the powder compositions referenced in FIG. 6.

FIG. 8 is a table showing results of the selective laser sinter jobsshown in FIG. 7B.

FIG. 9A is a chart showing the tensile properties of parts made via SLSfrom PEKK powder lots using different amounts of fines.

FIG. 9B is a chart comparing the tensile properties in the x-plane ofthe test parts made in the selective laser sinter jobs from a PEKKpowder from which fines have been removed (Traditional) and from a PEKKpowder in which fines have been reintroduced in accordance with thepresent invention (Fines).

FIG. 10 is a chart comparing the tensile properties in the z-plane ofthe test parts made in the selective laser sinter jobs from a PEKKpowder from which fines have been removed (Traditional) and from a PEKKpowder in which fines have been reintroduced in accordance with thepresent invention (Fines).

FIG. 11A is a chart comparing in-plane surface roughness of parts madevia the SLS process from a PEKK powder from which fines have beenremoved (Traditional) and from a PEKK powder in which fines have beenreintroduced in accordance with the present invention (Fines).

FIG. 11B is a chart comparing out-of-plane surface roughness of partsmade via the SLS process from a PEKK powder from which fines have beenremoved (Traditional) and from a PEKK powder in which fines have beenreintroduced in accordance with the present invention (Fines).

DETAILED DESCRIPTION

The present disclosure describes aspects of the present invention withreference to the exemplary embodiments illustrated in the drawings;however, aspects of the present invention are not limited to theexemplary embodiments illustrated in the drawings. It will be apparentto those of ordinary skill in the art that aspects of the presentinvention include many more embodiments. Accordingly, aspects of thepresent invention are not to be restricted in light of the exemplaryembodiments illustrated in the drawings. It will also be apparent tothose of ordinary skill in the art that variations and modifications canbe made without departing from the true scope of the present disclosure.For example, in some instances, one or more features disclosed inconnection with one embodiment can be used alone or in combination withone or more features of one or more other embodiments.

The present invention is especially useful for preparing polymer powdersfor laser sintering. One such class of polymer powders isPolyaryletherketones (“PAEK”) polymers. PAEKs are of interest in the SLSprocess because parts that have been manufactured from PAEK powder orPAEK granulates are characterized by a low flammability, a goodbiocompatibility, and a high resistance against hydrolysis andradiation. The thermal resistance at elevated temperatures as well asthe chemical resistance distinguishes PAEK powders from ordinary plasticpowders. A PAEK polymer powder may be a powder from the group consistingof polyetheretherketone (“PEEK”), polyetherketoneketone (“PEKK”),polyetherketone (“PEK”), polyetheretherketoneketone (“PEEKK”) orpolyetherketoneetherketoneketone (“PEKE KK”).

PEKKs are well-known in the art and can be prepared using any suitablepolymerization technique, including the methods described in thefollowing patents, each of which is incorporated herein by reference inits entirety for all purposes: U.S. Pat. Nos. 3,065,205; 3,441,538;3,442,857; 3,516,966; 4,704,448; 4,816,556; and 6,177,518. PEKK polymersdiffer from the general class of PAEK polymers in that they ofteninclude, as repeating units, two different isomeric forms ofketone-ketone. These repeating units can be represented by the followingFormulas I and II:-A-C(═O)—B—C(═O)—  I-A-C(═O)-D-C(═O)—  II

where A is a p,p′-Ph-O-Ph-group, Ph is a phenylene radical, B isp-phenylene, and D is m-phenylene. The Formula I:Formula II isomerratio, commonly referred to as the T:I ratio, in the PEKK is selected soas to vary the total crystallinity of the polymer. The T:I ratio iscommonly varied from 50:50 to 90:10, and in some embodiments 60:40 to80:20. A higher T:I ratio such as, 80:20, provides a higher degree ofcrystallinity as compared to a lower T:I ratio, such as 60:40.

The crystal structure, polymorphism, and morphology of homopolymers ofPEKK have been studied and have been reported in, for example, Cheng, Z.D. et al, “Polymorphism and crystal structure identification inpoly(aryl ether ketone ketone)s,” Macromol. Chem. Phys. 197, 185-213(1996), the disclosure of which is hereby incorporated by reference inits entirety. This article studied PEKK homopolymers having allpara-phenylene linkages [PEKK(T)], one meta-phenylene linkage [PEKK(I)],or alternating T and I isomers [PEKK(T/I)]. PEKK(T) and PEKK(T/I) showcrystalline polymorphism depending upon the crystallization conditionsand methods.

In PEKK(T), two crystalline forms, forms I and II, are observed. Form Ican be produced when samples are crystallized from melting at lowsupercooling, while Form II is typically found via solvent-inducedcrystallization or by cold-crystallization from the glassy state atrelatively high supercooling. PEKK(I) possesses only one crystal unitcell which belongs to the same category as the Form I structure inPEKK(T). The c-axis dimension of the unit cell has been determined asthree phenylenes having a zig-zag conformation, with the meta-phenylenelying on the backbone plane. PEKK(T/I) shows crystalline forms I and II(as in the case of PEKK(T)) and also shows, under certain conditions, aform III.

Suitable PEKKs are available from several commercial sources undervarious brand names. For example, polyetherketoneketones are sold underthe brand name OXPEKK® polymers by Oxford Performance Materials, SouthWindsor, Conn. Polyetherketoneketone polymers are also manufactured andsupplied by Arkema. In addition to using polymers with a specific T:Iratio, mixtures of polyetherketoneketones may be employed.

The powders used in these applications are produced by a variety ofprocesses such as grinding, air milling, spray drying, freeze-drying, ordirect melt processing to fine powders. The heat treatment can beaccomplished before or after the powders are produced, but if treatedprior to forming the powders, the temperature of the powder formingprocess must be regulated to not significantly reduce the meltingtemperature or the quantity of the crystallinity formed in the heattreatment process.

According to one embodiment of the present invention, in reference toFIG. 1, a LS system 10 in accordance with the present invention isillustrated. The system 10 includes a first chamber 20 having anactuatable piston 24 deposed therein. A bed 22 is deposed at an end ofthe piston 24. It should be understood that the term bed may refer tothe physical structure supported on the piston or the uppermost layer ofpowder deposed thereon.

The temperature of the bed 22 can be variably controlled via acontroller 60 in communication with heating elements (not shown) in oraround the bed 22. Furthermore, the LS system 10 according to theinvention may include a heating device (not shown) above the bed 22,which preheats a newly applied powder layer up to a working temperaturebelow a temperature at which the solidification of the powder materialoccurs. The heating device may be a radiative heating device (e.g., oneor more radiant heaters) which can introduce heat energy into the newlyapplied powder layer in a large area by emitting electromagneticradiation.

A second chamber 30 is adjacent to the first chamber 20. The secondchamber 30 includes a table surface 32 disposed on an end of a piston 34deposed therein. A powder 36 for use in the LS system 10 is stored inthe second chamber 30 prior to the sintering step. It will be understoodto a person of ordinary skill in the art and familiar with thisdisclosure that while a specific embodiment of a LS system is disclosed,the present invention is not limited thereto, and different known LSsystems may be employed in the practice of the present invention.

During operation of the LS system 10, a spreader 40 translates across atop surface of the first chamber 20, evenly distributing a layer ofpowder 36 across onto either the top surface of the bed 22 or thematerial previously deposed on the bed 22. The LS system 10 preheats thepowder material 36 deposed on the bed 22 to a temperature proximate to amelting point of the powder. Typically, a layer of powder is spread tohave a thickness of 125 μm, however the thickness of the layer of powdercan be increased or decreased depending on the specific LS process andwithin the limits of the LS system.

A laser 50 and a scanning device 54 are deposed above the bed 22. Thelaser 50 transmits a beam 52 to the scanner 54, which then distributes alaser beam 56 across the layer of powder 36 deposed on the bed 22 inaccordance with build data. The laser selectively fuses powder materialby scanning cross-sections generated from a three-dimensional digitaldescription of the part on the surface of the bed having a layer of thepowder material deposed thereon. The laser 50 and the scanner 54 are incommunication with the controller 60. After a cross-section is scanned,the bed 22 is lowered by one layer thickness (illustrated by thedownward arrow), a new layer of powdered material is deposed on the bed22 via the spreader 40, and the bed 22 is rescanned by the laser. Thisprocess is repeated until a build 28 is completed. During this process,the piston 34 in the second chamber is incrementally raised (illustratedby the upward arrow) to ensure that there is a sufficient supply ofpowder 36.

In the method of preparing the powders in accordance with the presentinvention, a raw PEKK flake is provided. The raw PEKK flake iscommercially available from companies such as Arkema, Inc. of King ofPrussia, Pa., and Cytec Industries Inc. of Woodland Park, N.J. The rawPEKK flake is typically swilled from a chemical reactor and then washed.The raw PEKK flake is a non-powder material. That is, the raw PEKK flakeis not in the form of a powder that can be used in the LS. The raw PEKKflake is in the form of irregularly-shaped particles (e.g., particlesthat are vaguely round, elongated, flat, etc.) and has an appearancesimilar to that of Rice Krispies® cereal. The irregularly-shapedparticles of the raw PEKK flake have grain sizes that are orders ofmagnitude larger than 150 μm, for example. The remainder of the raw PEKKflake can be in the form of a gel or gel-like form caused by an amountof liquid solvent remaining from the process of producing the raw PEKK.

After the step of providing the raw PEKK flake, a heat treatment step isoptionally performed that involves placing the raw PEKK flake into ashallow pan and heating both within a convection oven. The temperatureis ramped up to 200° C. over a one-hour period. The temperature is heldat 200° C. for several hours (e.g., 5 or 6 hours). The temperature isramped up a second time to 225° C. The temperature is held at 225° C.for a minimum of one hour and for preferably between one and four hours.The temperature is then ramped up a third time to 250° C. Thetemperature is held at 250° C. for a minimum of one hour and forpreferably between one and four hours. The heat treatment stepevaporates any remaining liquid solvent and causes at leastsubstantially all of the raw PEKK to be in the form ofirregularly-shaped particles. The heat treatment step also causes somecoalescence of the irregularly-shaped particles. However, the bulkdensity of the raw PEKK remains low after the heat treatment step.

After the heat-treating step, a cooling step is performed that involvespowering-off the convection oven and allowing the raw PEKK to coolnaturally.

The heat-treatment process is the subject of U.S. patent applicationSer. No. 15/872,478 filed on Jan. 16, 2018 by Hexcel Corporation andtitled “Polymer Powder and Method of Using the Same.” The disclosure ofthat reference is hereby incorporated by reference.

After the cooling step, a grinding or milling step is performed thatinvolves grinding the raw PEKK flake to form what will hereinafter bereferred to as the “PEKK powder.” The grinding step can be performedusing known grinding techniques performed by companies such as Aveka,Inc. of Woodbury, Minn. Upon completion of the grinding step, theparticles of the PEKK powder are significantly smaller (i.e., severaldegrees of magnitude smaller) than the particles of the raw PEKK. Theparticles of the PEKK powder are more consistent and regular in shape ascompared to the particles of the raw PEKK; however, the particles of thePEKK powder are still irregularly-shaped in comparison to thespherical-shaped particles.

A person of ordinary skill in the art and familiar with this disclosurewill understand that the grinding may also be referred to aspulverization, milling, or jet milling. In addition, a person ofordinary skill in the art and familiar with this disclosure willunderstand that it may also be employed with other polymer powders,including those in the PAEK family.

FIG. 2A is an image 200 showing magnified PEKK particles 202 after thegrinding process. These particles were ground from PEKK flake via jetmilling. For example, Aveka CCE Technologies based in Cottage Grove,Minn., USA provides grinding and classification services. A mill is usedthat incorporates dense phase micronization using turbulent, free jetsin combination with high efficiency centrifugal air classificationwithin a common housing. This provides comminution by high probabilityof particle-on-particle impact for breakage and a high degree ofparticle dispersion for separation. The resultant particles arenon-spherical and substantially angular. This is a result of the jetmilling process that performs particle comminution viaparticle-on-particle impact. The substantial non-spherical PEKKparticles perform better in the LS process. For example, thenon-spherical particles are more easily distributed on the bed table forthe LS process and the non-spherical particles result in substantiallystronger parts, particularly in the out-of-plane axis. The increasedperformance of non-spherical particles is due in part to the increasedability for larger and smaller particles to pack together enhancing thestrength of the laser fusion.

The raw PEKK flake is ground into a PEKK powder comprising a pluralityof PEKK particles. The PEKK particles range in size from less than 10 μmto about 200 μm. A person of ordinary skill in the art and familiar withthis disclosure will understand that the particle size range will varybased on the type of polymer being milled and the specific parameters ofthe milling process.

After the grinding, distribution of powder particles can be analyzedbased on particle size using a particle size distribution (“PSD”). Forexample, a PSD by particle volume shows the percentage of a volume of aspecific diameter particle range in the powder composition relative tothe overall volume of the composition. A PSD by particle count shows thepercentage of a particle count of a specific diameter particle range inthe powder composition relative to the overall particle count of thecomposition.

The PSD can be determined using the Coulter counter method (followingISO 13319). The Coulter method of sizing and counting particles is basedon measurable changes in electrical impedance produced by nonconductiveparticles suspended in an electrolyte. A small opening (aperture)between electrodes is the sensing zone through which suspended particlespass. The Coulter method enables the determination of particledistribution by size according to particle volume relative to theoverall volume of the sample or to particle count relative to theoverall count of particles in the sample. In reference to the PSD andgenerally in this application, the term particle diameter refers to agreatest dimension of the particle. A person of ordinary skill in theart and familiar with this disclosure will understand that in context ofthe particle size, the term diameter does not indicate that theparticles are spherical, but instead refers to a largest dimension ofthe particle as determined via the Coulter method. As discussed above,the plurality of PEKK particles are highly angular and substantiallynon-spherical due to the particle-on-particle contact impacts during thejet milling process.

After the milling, an air classification method may be used to separatefine particles from the milled PEKK powder. It is known in the art thatit is necessary to reduce or eliminate particles having a diameter belowa cutoff point, for example 30 μm, as it has been found that particlesin this range prevent use of the powder in the LS process. For example,International Patent Application WO2014100320 discloses such a methodfor preparing powders for use in selective laser sintering. It isunderstood in the art that parts cannot be manufactured in the SLSprocess from a powder wherein the fine particles have not been sievedfrom the powder. Such an unsieved powder causes pilling, sticking, andother forms of fouling in the powder application steps of the SLSprocess, and further results in curling and premature melting thatinhibit use of such powders in the SLS process.

In reference to FIGS. 3A and 3B two charts 300, 350 show informationrelating to a plurality of milled PEKK particles prior to removing thefines. Chart 300 shows a PSD by particle count of a milled PEKK powdercomposition for lot number X69865 prior to separating the fineparticles. Chart 350 shows a PSD by particle volume of the milled PEKKpowder composition shown in chart 300 prior to separating the fineparticles. The PSD by particle count 300, shown in FIG. 3A, shows therelatively large number of fine particles in the PEKK powder compositionprior to separation. In reference to chart 300, showing the PSD byparticle count, the plurality of particles have a mean diameter of 17.92μm, a median diameter of 13.19 μm, and a standard deviation of 12.94 μm,each determined based on the particle count. In reference to chart 350,showing the PSD by particle volume, the plurality of particles have amean diameter of 55.83 μm, a median diameter of 55.96 μm, and a standarddeviation of 26.88 μm, each determined based on the volume.

In reference to FIGS. 4A and 4B two charts 400, 450 show informationrelating to a plurality of fine PEKK particles removed from the PEKKpowder compositions illustrated in FIGS. 3A and 3B. In this case, a 30μm cutoff was used to separate the fines from the milled PEKK powder.Chart 400 shows a PSD by particle count of the fines separated from themilled PEKK powder composition for lot number X69865. Chart 450 shows aPSD by particle volume of the fines separated from the PEKK powdercomposition. In reference to chart 400, showing the PSD by particlecount for the removed fines, the plurality of particles have a meandiameter of 13.51 μm, a median diameter of 11.81 μm, and a standarddeviation of 5.34 μm, each determined based on the particle count. Inreference to chart 450, showing the PSD by particle volume, theplurality of particles have a mean diameter of 21.76 μm, a mediandiameter of 20.47 μm, and a standard deviation of 9.84 μm, eachdetermined based on the volume. The fines particles removed from themilled particles constitute between 15% and 25% of the milling, andtypically average 20%.

In reference to FIGS. 5A and 5B two charts 500, 550 show informationrelating to a plurality of the PEKK powder compositions illustrated inFIGS. 3A and 3B after the fines, shown in FIGS. 4A and 4B, have beenremoved. As indicated above, a 30 μm cutoff was used to separate thefines from the PEKK powder. Chart 500 shows a PSD by particle count ofthe PEKK powder composition after the fines are separated from the PEKKpowder composition for lot number X69865. Chart 550 shows a PSD byparticle volume of the PEKK powder composition after the fines have beenseparated. In reference to chart 500, showing the PSD by particle countafter removal of the fines, the plurality of particles have a meandiameter of 39.57 μm, a median diameter of 36.65 μm, and a standarddeviation of 18.67 μm, each determined based on the particle count. Inreference to chart 550, showing the PSD by particle volume, theplurality of particles have a mean diameter of 65.16 μm, a mediandiameter of 62.85 μm, and a standard deviation of 23.70 μm, eachdetermined based on the volume.

After the grinding and separation steps, a mixing step is performed toassemble the powder composition for laser sintering. The inventors havediscovered that they can overcome the disadvantages associated withperforming SLS on feedstocks with fine particles if they separate thefine particles from the feedstock and subsequently reincorporate theminto the feedstock using a mixer at or around the time that carbon fiberis also introduced into the powder composition. The inventors haveunexpectedly discovered that parts made via the SLS process from suchimproved powders include superior tensile properties in both the x andthe z direction as compared to parts made using SLS from ESD withoutfines and that such parts made from the improved powders includeimproved smoothness in both upskin and downskin surfaces as compared tosimilar parts made from ESD powder without fines. In addition, the SLSprocess using the powder in accordance with the present invention is upto 33% more cost efficient because the previously discarded PEKK finespowder can now be used in the SLS process.

In some embodiments of the present invention, three fractions are mixedtogether to form the powder composition for selective laser sinter,which may be referred to ESD+fines. ESD refers to a standard PEKK powdercomposition offered by Hexcel with 85% PEKK powder and 15% carbon fiberby weight. Fine particles have been removed from the ESD powder.Therefore, it may also be referred to as ESD+no fines. ESD+fines refersto the above described ESD powder in which fines have been removed fromthe milled powder and then reintroduced.

In some embodiments, the powder compositions comprises three fractionsthat include a first fraction, a second fraction, and a third fraction.The first fraction comprises a plurality of fine PEKK particles. Thesecond fraction comprises a plurality of PEKK particles from which thefines have been previously removed. The third fraction comprises aplurality of carbon fibers. The first and second fraction may be fromthe same lot of powder that was milled or may be different lots ofpowder.

The percentage by weight of the first fraction to the overall powdercomposition can vary between 5% and 25% or greater. In some embodiments,the first fraction of fines typically constitutes between 10% and 20% ofthe powder composition by weight. The examples shown below indicate thata first fraction of 10% by weight may yield optimal strength andbuilding conditions under the conditions set forth in those examples. Inone embodiment of the present invention, the plurality of particles ofthe first fraction having a mean diameter as determined by particlecount less than 30 microns. In another embodiment of the presentinvention, the plurality of particles of the first fraction have a meandiameter as determined by particle count between 10 μm to 20 μm.

In some embodiments, the percentage by weight of the second fraction tothe overall powder composition can vary between 55% and 85% or greater.In other embodiments of the present invention, the non-fines constitutebetween 65% and 75% of the powder composition by weight. In oneembodiment of the present invention, the plurality of particles of thesecond fraction has a mean diameter as determined by particle countgreater than 30 microns. In another embodiment of the present invention,the plurality of particles of the first fraction have a mean diameter asdetermined by particle count between 10 μm to 20 μm.

The third fraction combined during the mixing process includes an amountof carbon fiber. The addition of the carbon fiber has the effect ofreinforcing and/or stiffening the resulting object. In addition, thecarbon fiber may serve as an agent to improve the distribution of PEKKparticles, including the fine particles, on the surface of the lasersintering bed. They may enhance the flow of the particles and preventproblems associated with fines in some cases. In the embodimentsdisclosed use of carbon fiber with an average length L50 is greater thanthe average grain size D50 of the PEKK powder particles. In someembodiments, PEKK powder and carbon fibers can be selected such thatD50<L50<D90.

In some embodiments of the present invention, the first fraction, thesecond fraction, and the third fraction are mixed at the same time toform the powder composition. The carbon fiber and the PEKK powder,including the fines fraction, can be mixed using a heat shear processthat involves mixing the three components using high speed, high torquemixing elements (e.g., a Henschel Mixer®). This has the effect offorcibly dispersing fiber clumps. If left intact, these clumpsnegatively impact both electrical behaviors and mechanics of themixture. The more commonly used tumbling blenders (e.g., V-typeblenders) lack the energy to disperse fibers correctly. It can beadvantageous to prepare large batches of the PEKK powder and carbonfiber mixture for the sake of reducing variability in the processes.

In accordance with one embodiment of the present invention carbon fiberavailable from Hexcel Corporation of Stamford, Conn., USA and sold underthe brand name HEXTOW® AS4 is employed. The carbon fiber is acontinuous, high strength, high strain, PAN based fiber. In thisembodiment, the carbon fiber has a filament diameter of approximately7.1 μm and is wound on a cardboard tube. It should be understood to aperson having ordinary skill in the art that different types and brandsof carbon fibers may be employed, and that the present invention is notspecifically limited in this regard.

The carbon fiber is milled prior to incorporation into the PEKK powderto achieve the desired carbon fiber length as determined by the averageL50. The carbon fiber is milled by a miller such as E&L Enterprises Inc.in Oakdale, Tenn., USA. For example, in one embodiment of the presentinvention, the mean carbon length, L50, is 77 μm. The minimum lengthmeasured is 38.15 μm, the maximum length measured is 453 μm, and thestandard deviation is 42.09 μm. In one embodiment, the milled carbonfiber included in the powder has a mean length L50 is greater than themean diameter of the plurality of particles D50. In some embodiments,the L50 is greater than 70 μm. In some embodiments of the presentinvention, the L50 of the carbon fiber is between 70 μm and 90 μm. Inyet other embodiments of the present invention, the average fiber lengthL50 is between 70 μm and 80 μm.

A powder composition suitable for use in a selective laser sintering forprinting a three-dimensional object is prepared combining a PEKK powderwith the carbon fiber. In some embodiments of the present invention thecomposition includes 85% by weight of PEKK powder and 15% by weightcarbon fiber. It yet other embodiments of the present invention, theamount of carbon fiber is varied relative to the polymer powder toachieve composition for SLS. In some embodiments of the presentinvention, one or more additives are added to the matrix to affect theproperties of the SLS composition, for example, during the printingprocess or in the printed article. It will be understood to a person ofordinary skill in the art and familiar with this invention, that theratio of carbon to polymer may vary and the above examples are providedfor illustration purposes. The polyaryletherketone (PAEK) powder has aplurality of particles having a mean grain size D50. A plurality ofcarbon fibers have a mean length L50. L50 is greater than D50.

The plurality of carbon fibers and the plurality of PEKK particles,including the fines and non-fines fractions, are mixed in a highintensity mixer. This may include the Henschel FM 200 high intensitymixer offered by Zeppelin. In the process of high intensity mixing thecarbon fibers and PEKK particles are accelerated at high speeds causingcollisions between the fibers and the particles thereby embedding thefibers into the PEKK particles. For example, a composition in accordancewith the present invention was prepared using a high energy mixer(Zeppelin FM-200) that ran 7 minutes per batch (maximum 100 lbs. fit inthe mixer) and the slowest speed is 600 RPM. It has been discovered thatembedding the carbon fiber into the particles via the high intensitymixing method results in a portion of the fiber in the particle and aportion of the fiber outside the particle. This configuration has beenshown to significantly increase the mechanical properties of parts madefrom the composition powder using the LS method.

In reference to FIG. 2B an image showing magnified views of a pluralityof PEKK particles and a plurality of carbon fibers after completion ofthe high energy mixing. As shown in the image, at least a portion of theplurality of the carbon fibers are at least partially embedded in theplurality of particles of the PAEK powder and a least a portion of thecarbon fiber is protruding therefrom.

By using the fines in the process, it is possible to increase the yieldof powder composition from the raw PEKK flake. As discussed in furtherdetail below, the addition of the fines increases the strength of theparts, and reduces surface roughness, among other benefits. In someembodiments of the present invention it may be possible to omit theseparation step. In such cases, the fines are not separated and thecarbon is blended with the powder composition that already includes thefines. This method was also tested, as discussed below, resulting in onepowder lot that was useable in the SLS process and a second powder lotthat was unusable in the SLS process. It has been observed that this maybe due to the fact that the separation process results in more uniformblend of fines and non-fines thereby providing a more consistent powdercomposition product that is more susceptible to predictable sintering.

EXAMPLES

In reference to FIGS. 6, 7A, 7B, and 8, tables are provided withqualification data of powder compositions prepared in accordance withthe present invention and parts made therefrom via the selective lasersinter process. In reference to FIGS. 9A, 9B and 10 data is shown thatillustrates than unexpected increased tensile strength and unexpectedimproved surface finish in parts made via SLS from the inventive powdercomposition as compared to parts made from an ESD powder without fines.

In reference to table 700 in FIG. 7A a plurality of powder compositionsare identified by unique lot numbers in the column identified with theheader “Lot #.” Each of the powder compositions comprises a firstfraction of fines PEKK powder, a second fraction of non-fines PEKKpowder, and a third fraction of carbon fiber. The raw PEKK flake had aT:I ratio of 60:40 and was supplied by either Arkema, Inc. of King ofPrussia, Pa., or Cytec Industries Inc. of Woodland Park, N.J., as isshown in the column in table 700 identified with the head “Supplier.”

In each qualification example, the raw PEKK flake was subject to a heattreatment step to remove impurities from the PEKK flake. As describedabove, the temperature was ramped up to 200° C. over a one-hour period.The temperature was then held at 200° C. for about six hours. Thetemperature was then ramped up a second time to 225° C. The temperaturewas then held at 225° C. for a minimum of one hour. The temperature wasthen ramped up a third time to 250° C. and held for at least one hour.

After heat treatment, each of the PEKK flake lots was milled by jetmilling resulting in a plurality of particles ranging in size from lessthan 10 μm to about 200 μm. The milling process was performed using 3000lbs. lots of PEKK flake. After milling air classification was used toseparate fine particles from the milled lots. The classification was setto remove particles having a diameter of 30 μm or less from each lot.This is referred to as fines material, whereas the remainder of themilled lot may be referred to a non-fines material. The removed finesmaterial was about 20% of the total mass of the milled PEKK flake.

Each of the lots shown in table 700 were mixed in a Zeppelin FM-200mixer that ran 7 minutes per batch (maximum 100 lbs. fit in the mixer)and the slowest speed is 600 RPM. In each lot a first fraction of finespowder was added, a second fraction of non-fines powder was added, and athird fraction of carbon fiber was added. In each of the examples, thecarbon fiber was 15% by weight of the resultant powder composition. Thepercentage of fines was varied in each case. In reference to table 700in FIG. 7A, the column identified with the header “% Fines (total PEKK)”identifies the percentage of fines PEKK material relative to the overallamount of PEKK material by mass. For example, in reference to the LotX5470S-6013M, the percentage of fines relative to the overall amount ofPEKK in the composition was 22.3%. Thus, if there was 100 lbs. of lotX5470S-6013M, it would include 15 lbs. of carbon fiber and 85 lbs. ofPEKK powder material, of which 16.72 lbs. was fines PEKK powder, or22.3% of 85 lbs. In the tested powder compositions, the percentage offines reintroduced into the sieved ESD power varied between 24% of theoverall PEKK in the mixture to 10% of the overall PEKK in the mixture.

In each of the qualification examples, the fines had a mean size of lessthan 30 μm, and more specifically a mean size between 10 μm and 20 μmdetermined from the PSD based on the particle count. The non-fines had amean size greater than 30 μm and more specifically a mean size between40 μm and 70 μm.

In further reference to table 700 shown in FIG. 7A, the supplier of thePEKK flake is identified in the column identified with the header“Supplier.” In the examples shown in table 700 the supplier isidentified as Arkema or Cytec. The condition of the blended powder isalso identified, namely virgin or recycled, in the column identifiedwith the head “Condition.” Type I refers to virgin powder or powder thathas never been subject to a SLS process, and Type II refers to Cake A orpowder that has been used in one previous SLS process. The columnidentified with the header “Compound/Blend” identifies a referencenumber associated with the blending of the first fraction, secondfraction, and third fraction to obtain the powder composition for theSLS process. The column identified with the header “Build Job #”identifies a selective laser sinter print job for each Lot # of powder.In the examples, some of the powder compositions were tested in two ormore separate builds hence there are two or more build job numbersassociated with each lot and identified in Table 700. The columnidentified with the header P800 identifies the EOS P800 selective lasersinter machine on which the print job was performed. In the cases ofmultiple print jobs for a lot of powder, multiple corresponding machinesare identified.

In further reference to Table 700 shown in FIG. 7A, the percentage offines relative to the overall PEKK powder material in the composition isnot shown for lots X0000S-6483MA and X0000S-7000MA. In these powdercompositions a percentage of fines is not available because the lotcomprises recycled PEKK material. Recycled PEKK material has previouslybeen used in an SLS process but not formed into an object. In bothcases, the original PEKK that was used to form the recycled materialincluded between 15% and 25% of fines material relative to the overallmass of PEKK material in the powdered composition. This fines materialwas removed via sieving and reintroduced into the powder composition inaccordance with the present invention.

In reference to FIG. 6, table 600 is shown. Table 600 illustratesdifferent properties of the tested lots of PEKK material as determinedfrom the blended powder compositions. DSC analysis was used to determinethe properties. The test results for each lot of powder were compared toacceptance criteria, which is shown in the bottom row of table 600.Specifically, the acceptance criteria required a glass transitiontemperature between 154 and 167 degrees Celsius and an FTIR percentageof match to a standard greater than 95%. As shown in table 600 in FIG.6, each of the lots of PEKK powder with carbon and fines satisfied thestated criteria.

In further reference to Table 600, the column identified with “MeltingTransition Temperature” identifies a melting point for each lot ofpowder. Two melting points are identified for lots comprising virginpowder because PEKK is a polymorph material that exhibits two meltingpoints. However, after the PEKK material is recycled it typicallyexhibits a single melting point in DSC analysis. This is shown inreference to the two lots denoted with asterisks in Table 600 as each ofthese lot comprises PEKK material that has been subject to at least oneSLS build.

In order to test the powder compositions in the SLS process an SLS printjob was performed using each powder composition to print testingspecimens in accordance with ASTM D638. ASTM D638 is a common plasticstrength specification and covers the tensile properties of unreinforcedand reinforced plastics. The test method uses standard “dumbbell” or“dogbone” shaped specimens that are tested on a tensile testing machine.For each powder composition at least five test specimens weremanufactured in the in-plane direction, also referred to as thex-direction, and at least five test specimens were manufactured in theout-of-plane direction or the z-direction. Each of the test specimenswere tested pursuant to ASTM D638 and the results for each direction foreach powder were averaged. The average results are provided as Table 800shown in FIG. 8.

For each tested powder composition, the SLS builds were performed in aP800 machine. Table 750 in FIG. 7B shows build parameters. In the rowidentified with the header “Process Chamber Temperature,” the processchamber temperature, also referred to sometimes as the bed temperature,is shown for each build. The process chamber temperature for each powdercomposition was determined in accordance with an analytical method fordetermining the bed temperature of an SLS machine. That method is thesubject of US patent publication no. US20150061195 by Hexcel Corporationand titled “Method For Analytically Determining SLS Bed Temperatures.”The disclosure of that reference is hereby incorporated by reference.Table 750 shows the consistency of process chamber temperature, dosingfactors and exposures between each build. Supported by historicalpractices, it is important to note that Type II (Cake A) material runsat a higher temperature (299) and exposure setting; builds 6574 and 7004were Type II material.

The laser power, or exposure, for each qualification build is shown inTable 750 in the row identified with exposure. The laser exposure wasdetermined in accordance with an analytical method disclosed in U.S.patent application Ser. No. 15/872,496 filed on Jan. 16, 2018 by HexcelCorporation and titled “Method for Analytically Determining Laser Powerfor Laser Sintering.” The disclosure of that reference is herebyincorporated by reference. In each case, the exposure number correspondsto a power wattage of the laser wherein an Exposure [ESDCON] of 5corresponds to 14 Watts, an Exposure [ESDCON] of 6 corresponds to 13.5Watts, an Exposure [ESDCON] of 7 corresponds to 13.0 Watts, an Exposure[ESDCON] of 8 corresponds to 12.5 Watts, an Exposure [ESDCON] of 9corresponds to 12.0 Watts, an Exposure [ESDCON] of 10 corresponds to11.5 Watts, an Exposure [ESDCON] of 8 corresponds to 12.5 Watts and anExposure [ESDCON] of 20 corresponds to 6.5 Watts.

In FIG. 8, a table 800 showing performance properties for thequalification builds is provided with reference to job number. FIG. 8also includes acceptance criteria determined from applicant's testlibrary using ESD powder from which the fines have been separated. FIG.8 also includes the averages of all ESD+fines powdered tested in thestudy and historical data of Hexcel's ESD powder without fines. Table800 includes the following information for each tested powdercomposition: Glass Transition Temperature (Tg), FTIR % Match, SpecificGravity, Average Tensile Stress at Break (X, Z), Average Elongation (X,Z) and Average, Young's Modulus of Elasticity (X, Z). The averagetensile strength, elongation and Young's Modulus of Elasticity weredetermined using the aforementioned ASTM D638 protocol. It is importantto note that Type II (Cake A) (6574, 7004) should show higher mechanicalperformance characteristics due to the fact that recycled PEKK powder isknown to result in stronger parts.

The third row from the bottom shows the average fines data of the ESDfines lots tested. This omits job numbers 6574 and 7004 to ensure anaccurate comparison as those lots comprise recycled powder. The secondrow from the bottom is identified with the header Non-Fines Average.This information is historical data collected by Hexcel Corporationbetween 2016 and 2017 for its commercial production of SLS builtproducts using the P800 machines using a powder composition consistingessentially of 85% PEKK powder from which fines having a size less than30 μm have been removed and 15% carbon fiber. The powder compositions donot include recycled material. The test parts in the non-fines powderwere built in accordance with the same analytical techniques used inconstruction of the fines qualification pieces using the same group ofP800 sintering machines.

The qualification builds with the fines plus powder consistentlysatisfied the acceptance criteria. The Applicant was unexpectedly ableto use the PEKK powder composition with fines to repeatedly build partsusing the SLS process that satisfied its rigid acceptance criteria. Whencomparing the fines-plus data against non-fines, it is also observed thefines plus material results in parts that were unexpectedly stronger asdemonstrated by the tensile tests and unexpectedly smooth. The fact thatthe fines could be used in a PEKK composition in SLS is also unexpectedbecause it was previously understood and previously demonstrated byApplicant that fines powder could not be used in the SLS process toprint parts. Therefore, the present invention results in a significantcost savings over the prior art. There is a potential to increase theyield of raw flake by 30% and reduce the cost of raw material in acommensurate amount. The fines powder in accordance with the presentinvention results in SLS parts that maintains mechanical properties;tensile modulus, strength, and elongation show adequate results with theaddition of fines. The data shows an unexpected increase in tensilestrength in both X and Z directions. Data showing there is no effect onmodulus in X or Z. Data shows there is no effect on elongation as well.

As stated above, the test results indicate an increase of tensilestrength in the x-direction and the z-direction. In reference to FIG.9B, a chart 950 showing a summary of the tensile results in thex-direction is shown comparing tensile results for non-fines with carbonfiber powder composition 920 to fines with carbon fiber powder 910composition based on the above described test results. Parts made fromthe powder composition including fines showed a 7.5% increase instrength relative to the traditional or non-fines powder composition.The fines composition also showed a 27.0% reduction in the standarddeviation among tested parts. In reference to FIG. 10, a chart showing asummary of the tensile results in the z-direction is shown comparingtensile results for non-fines with carbon fiber powder composition 1020to fines with carbon fiber powder composition 1010 based on the abovedescribed test results. Parts made from the powder composition includingfines showed in 10.9% increase in strength relative to the traditionalor non-fines powder composition. The fines composition also showed a19.2% reduction in the standard deviation among tested parts.

In reference to FIG. 9A, table 900 showing the average tensileproperties of powder compositions in accordance with the presentinvention having 20% fines, 15% fines, and 10% fines reintroduced intothe milled particle as determined by the overall PEKK in thecomposition. The chart also shows average historical data for PEKK ESDpowder excluding the fines (0%). The test results are for powderprovided from a single supplier. The tensile test results on the builtparts show for powder from this supplier that reintroducing 10% of finespowder by weight of the total PEKK results in the strongest average partas measured in the Z-direction. Reintroduction of 15% fines by weight ofthe total PEKK results in the second strongest average, andreintroduction of 20% fines by weight of the total PEKK results in thethird strongest average. It should be noted that the 20% reintroductionwas still stronger than parts made from PEKK powder from which the fineswere removed.

Test parts were also constructed during the builds using the powdercompositions. The dimensional evaluation of these builds shows that theprofile and thickness dimensional values are in-line with currentproducts. The resistivity of the parts was also tested, and it was foundthat the resistivity is unaffected by the fines and that there is norelationship between added fines and resistivity.

In reference to FIGS. 11A and 11B, the average surface roughness of thequalification samples is shown and compared to the average surfaceroughness of the non-fines test pieces. The surface roughness is shownas an RMS value and was determined pursuant to ASME B46.1. In referenceto chart 1100 in FIG. 11A, the in-plane surface roughness is shown. Thisrefers to the x-plane in the build machine. Both the upskin, or toplayer, and downskin, or bottom layer, exhibits a substantial decrease insurface roughness between the PEKK powder composition without fines andthe powder composition with fines. Likewise, in reference to FIG. 11B,the out-of-plane surface roughness is shown. This refers to parts madealong the z-axis in the build machine. Both the first side and thesecond sides show a decrease in the surface roughness between the PEKKpowder composition without fines and the PEKK powder composition withfines.

While the present teachings have been described above in terms ofspecific embodiments, it is to be understood that they are not limitedto those disclosed embodiments. Many modifications and other embodimentswill come to mind to those skilled in the art to which this pertains,and which are intended to be and are covered by both this disclosure andthe appended claims. It is intended that the scope of the presentteachings should be determined by proper interpretation and constructionof the appended claims and their legal equivalents, as understood bythose of skill in the art relying upon the disclosure in thisspecification and the attached drawings.

What is claimed is:
 1. A powder composition suitable for use in lasersintering for printing a three-dimensional object, the powdercomposition comprising: a first fraction comprising apolyaryletherketone (PAEK) powder having a plurality of particles, theplurality of particles having a mean diameter less than 30 μm; a secondfraction comprising a PAEK powder having a plurality of particles, theplurality of particles having a mean diameter greater than 30 μm; athird fraction comprising a plurality of carbon fibers.
 2. The powdercomposition of claim 1, wherein the first fraction and the secondfraction comprise polyetherketoneketone (PEKK) particles.
 3. The powdercomposition of claim 2 wherein the plurality of particles of the firstfraction have a mean diameter between 10 μm to 20 μm.
 4. The powdercomposition of claim 3, wherein the third fraction is between 10% and20% of the composition by weight.
 5. The powder composition of claim 4,wherein the first fraction is between 5% and 25% of the composition byweight.
 6. The powder composition of claim 3, wherein the third fractionis 15% of the composition by weight.
 7. The powder composition of claim6, wherein the first fraction is 17% or less of the composition byweight.
 8. The powder composition of claim 4, wherein the PEKK particlesare substantially non-spherical.
 9. The powder composition of claim 8,wherein a mean length of the plurality of carbon fibers is greater thana mean diameter of the plurality of particles of the powder composition.10. The powder composition of 7 wherein the first fraction is 15% orless of the composition of by weight.
 11. The powder composition ofclaim 10, wherein the first fraction is 12.5% or less of the compositionby weight.
 12. The powder composition of claim 11, wherein the firstfraction is about 8.5% of the composition by weight.
 13. A threedimensional object obtained from a polyaryletherketone (PAEK) powder byselective laser sintering by applying a layer of the powder on a bed ofa laser sintering machine, solidifying selected points of the appliedlayer of powder by irradiation, successively repeating the step ofapplying the powder and the step of solidifying the applied layer ofpowder until all cross sections of the three-dimensional object aresolidified, wherein the powder has the following structuralcharacteristics: a first fraction separated from a polyaryletherketone(PAEK) feedstock, the first fraction comprising a plurality of particleshaving a mean diameter less than 30 μm; a second fraction separated fromthe PAEK feedstock, the second fraction comprising a plurality ofparticles having a mean diameter greater than 30μ; a second fractioncomprising a PAEK powder having a plurality of particles, the pluralityof particles having a mean diameter greater than 30 μm; a third fractioncomprising a plurality of carbon fibers; wherein the first fraction, thesecond fraction, and the third fraction are blended to obtain thepowder.
 14. The three dimensional object according to claim 13, whereinPAEK powder comprises polyetherketoneketone (PEKK).
 15. The threedimensional object according to claim 13, wherein the plurality ofparticles of the first fraction have a mean diameter between 10 μm to 20μm.
 16. The three dimensional object according to claim 15, wherein thethird fraction is between 10% and 20% of the composition by weight ofthe blended powder.
 17. The three dimensional object according to claim16, wherein the first fraction is between 10% and 25% of the compositionby weight of the blended powder.
 18. The three dimensional objectaccording to claim 17, wherein the third fraction is 15% of thecomposition by weight.
 19. The three dimensional object according toclaim 16, wherein the first fraction is 17% or less of the of thecomposition by weight of the blended powder.
 20. The three dimensionalobject according to claim 14, wherein the PEKK particles beingsubstantially non-spherical.
 21. The three dimensional object accordingto claim 20, the first fraction, the second fraction, and the thirdfraction are blended in a high intensity mixer.
 22. The threedimensional object according to claim 21 wherein blending comprisesoperating the high intensity mixer at a speed of greater than 500 rpmfor at least one minute.
 23. The three dimensional object according toclaim 21 wherein the PAEK feedstock is subject to a heat treatmentbefore the separation.
 24. The three dimensional object according toclaim 19, the first fraction is 15% or less of the composition of byweight.
 25. The three dimensional object according to claim 24, whereinthe first fraction is 12.5% or less of the composition by weight. 26.The three dimensional object according to claim 25, wherein the firstfraction is about 8.5% of the composition by weight.